This invention relates to data storage devices.
One known data storage device is a magnetic disk drive, in which data stored on one or more rotatable storage media are read and/or written by corresponding transducers supported on xe2x80x9csliders.xe2x80x9d As the media rotate, the resulting air stream elevates the sliders, and hence the transducers, slightly from the media surfaces. The fly height is relatively small, however, and thus the transducers may collide with, and become damaged or destroyed by, asperities, i.e., surface defects, on the storage media.
This invention features ways of avoiding collisions between a transducer and asperities on the surface of a data storage medium.
In a general aspect of the invention, information that indicates locations of the asperities on the surface of a moving data storage medium is provided, and relative movement between the transducer and the surface is altered in response to the information.
Preferred embodiments may include one or more of the following features.
In an idle mode of operation in which the transducer does not exchange data signals with the storage medium, the relative movement is altered by positioning the transducer over a portion of the surface that does not include an asperity during the movement of the storage medium. Preferably, the data are stored on tracks of the storage medium, and the information indicates a track on which an asperity is located. In the idle mode, the transducer is positioned over a track other than the indicated track, or a track nearby the indicated track.
Several ways of altering the movement are provided for a data exchange mode of operation in which the transducer is moved to a position over one of the tracks, performs a data exchange operation between the transducer and storage locations on the one track as the storage medium moves, and is thereafter moved away from the one track.
For example, if the track indicated by the information is the one track involved in the data exchange operation or is nearby that track, the transducer is moved over the one track or away from the one track to avoid colliding with the asperity. In one approach, the transducer is moved over the one track later than a nominal time before the data exchange operation is performed to avoid colliding with the asperity. Alternatively, the transducer is moved away from the one track earlier than a nominal time after the data exchange operation is performed to avoid colliding with the asperity. The relative movement between the transducer and the medium is altered differently if the data exchange operation is a read operation than if the data exchange operation is a write operation.
In another approach, the transducer is moved away from the one track as the asperity approaches the transducer, and then returned to the one track after the asperity passes the transducer. The amount of movement is sufficient to cause a selected region of the transducer to miss the asperity. For example, the transducer comprises a magnetoresistive element and adjacent magnet elements, and the selected region comprises the width defined by the magnetoresistive element and the magnet elements.
The relative movement between the transducer and the storage medium is also varied in response to the information in a seek mode of operation during which the transducer is moved from a position over a first one of the tracks along a selected trajectory to a position over a second one of the tracks as the storage medium moves. If the track indicated by the information is one that will be encountered by the transducer during the seek, the trajectory of the transducer is changed from the selected trajectory to avoid colliding with the asperity on the indicated track.
In one approach, the trajectory is changed by moving the transducer faster or slower than normal between the first and second tracks. For example, if the indicated track is between the first and second tracks, the trajectory is changed so that the transducer avoids the asperity as it crosses the indicated track. If the indicated track is the second track, the trajectory is changed so that the transducer arrives at the second track later than normal to avoid the asperity.
Preferably, the data storage medium moves by rotation. In one embodiment, the data storage medium and the transducer are magnetic devices. In another embodiment, the medium and the transducer are near field optical devices.
The data storage medium may have a second surface and a second transducer associated therewith, in which case the information indicates locations of the asperities on the second surface, and the relative movement between the second transducer and the second surface is altered in response to the information.
The data storage apparatus may include a plurality of moving storage media each of which has an associated transducer. The information indicates locations of the asperities on the surface of each one of the storage media, and the relative movement between the transducers and the surfaces are altered in response to the information. In embodiments in which the storage media move by rotation and data are stored on circular tracks thereof, corresponding tracks of the storage media define a cylinder, and the information indicates that a cylinder contains an asperity if any of the tracks thereof contain an asperity. Preferably, the relative movement of the transducers is altered in unison in response to the information to avoid an asperity in the cylinder.
The information is stored in a memory. The memory includes a record for each of the asperities that indicates the location thereof. In particular, each record indicates the track and sector on which the associated asperity is located. Each record may also store further information that indicates a characteristic (e.g., size or persistence) of the associated asperity. An output signal produced by the transducer is processed accordance with such further information.
A detector detects whether a change has occurred in one of the asperities and, if so, the corresponding record is updated in accordance with the change. The change includes, for example, an appearance of a new asperity, in which case a new record is created in the memory. If the detected change is the dissipation of a previously existing asperity, the corresponding record is deleted.
An asperity is detected by moving the transducer over the surface of the storage medium and determining the transducer collides with an asperity based on an output signal produced by the transducer.
Among other advantages, reducing collisions between the transducer and surface asperities reduces damage to the transducer that repeated collisions can cause. As a result, performance is enhanced, because noise that is often produced by a collision-damaged transducer is reduced. In addition, transducer operating lifetime is increased.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.